Reducing context coded and bypass coded bins to improve context adaptive binary arithmetic coding (CABAC) throughput

ABSTRACT

Techniques for context-adaptive binary arithmetic coding (CABAC) coding with a reduced number of context coded and/or bypass coded bins are provided. Rather than using only truncated unary binarization for the syntax element representing the delta quantization parameter and context coding all of the resulting bins as in the prior art, a different binarization is used and only part of the resulting bins are context coded, thus reducing the worst case number of context coded bins for this syntax element. Further, binarization techniques for the syntax element representing the remaining actual value of a transform coefficient are provided that restrict the maximum codeword length of this syntax element to 32 bits or less, thus reducing the number of bypass coded bins for this syntax element over the prior art.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 13/862,458, filedApr. 14, 2013, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/623,778, filed Apr. 13, 2012, U.S. ProvisionalPatent Application Ser. No. 61/641,997, filed May 3, 2012, U.S.Provisional Patent Application Ser. No. 61/650,023, filed May 22, 2012,and U.S. Provisional Patent Application Ser. No. 61/659,205, filed Jun.13, 2012, all of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention generally relate to contextadaptive binary arithmetic coding (CABAC) of syntax elements in videocoding.

Description of the Related Art

Video compression, i.e., video coding, is an essential enabler fordigital video products as it enables the storage and transmission ofdigital video. In general, video compression techniques applyprediction, transformation, quantization, and entropy coding tosequential blocks of pixels in a video sequence to compress, i.e.,encode, the video sequence. Video decompression techniques generallyperform the inverse of these operations in reverse order to decompress,i.e., decode, a compressed video sequence.

Context-adaptive binary arithmetic coding (CABAC) is a form of entropycoding used in video encoding. CABAC is an inherently losslesscompression technique notable for providing considerably bettercompression than most other encoding algorithms used in video encodingat the cost of increased complexity. In brief, CABAC has multipleprobability modes for different contexts. It first converts allnon-binary symbols to binary symbols referred to as bins. Then, for eachbin, the coder selects which probability model to use, and usesinformation from nearby elements to optimize the probability estimate.Arithmetic coding is then applied to compress the data. The theory andoperation of CABAC coding for H.264/AVC is defined in the InternationalTelecommunication Union, Telecommunication Standardization Sector(ITU-T) standard “Advanced video coding for generic audiovisualservices” H.264, revision March 2005 or later, which is incorporated byreference herein. General principles are explained in “Context-BasedAdaptive Binary Arithmetic Coding in the H.264/AVC Video CompressionStandard,” Detlev Marpe, July 2003, which is incorporated by referenceherein.

CABAC is a well known throughput bottleneck in video codecimplementations (particularly on the decoder side) primarily due to datadependencies in context selection which make CABAC difficult toparallelize. In CABAC, bins can be either context coded or bypass coded.Bypass coded bins do not require context selection which allows thesebins to be processed at a much high throughput than context coded bins.Thus, to improve the throughput of the CABAC, the number of contextcoded bins should be reduced. However, it is also desirable to reducethe number of bypass coded bins as the number of bypass coded bins arean order of magnitude larger than the number of context coded bins. Ingeneral, encoder and decoder hardware is designed for the worst case.Thus, it is important to reduce the worst case number of both contextand bypass coded bins.

SUMMARY

Embodiments of the present invention relate to methods, apparatus, andcomputer readable media for context adaptive binary arithmetic coding(CABAC) of certain syntax elements. In one aspect, a method for encodinga video sequence in a video encoder to generate a compressed video bitstream is provided that includes determining a value of a deltaquantization parameter syntax element, binarizing the value to generatea sequence of bins, wherein the sequence includes a prefix and a suffix,context coding the bins of the prefix into the compressed video bitstream, and bypass coding the bins of the suffix into the compressedvideo bit stream.

In one aspect, a method for decoding a compressed video bit stream in avideo decoder is provided that includes context decoding a firstsequence of bins from the compressed video bit stream, the firstsequence of bins corresponding to a prefix of a binarized value of adelta quantization parameter syntax element, debinarizing the firstsequence of bins to determine a value of the prefix, bypass decoding asecond sequence of bins from the compressed video bit stream, the firstsequence of bins corresponding to a suffix of the binarized value of thedelta quantization parameter syntax element, debinarizing the secondsequence of bins to determine a value of the suffix, and adding theprefix and the suffix to determine a value of the delta quantizationparameter syntax element.

In one aspect, a method for encoding a video sequence in a video encoderto generate a compressed video bit stream is provided that includesdetermining a value of a syntax element for a remaining actual value ofa transform coefficient, binarizing the value using a variable lengthcode (VLC) to generate a sequence of bins, wherein a maximum codewordlength of the VLC is 32 bits or less, and bypass coding the sequence ofbins into the compressed video bit stream.

In one aspect, a method for decoding a compressed video bit stream in avideo decoder is provided that includes bypass decoding a sequence ofbins from the compressed video bit stream, the sequence of binscomprising a prefix and a suffix of a binarized value of a syntaxelement for a remaining actual value of a transform coefficient, anddebinarizing the sequence of bins using a variable length code (VLC) todetermine a value of the syntax element, wherein a maximum codewordlength of the VLC is 32 bits or less.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments will now be described, by way of example only,and with reference to the accompanying drawings:

FIGS. 1A and 1B are block diagrams illustrating CABAC encoding anddecoding;

FIGS. 2A and 2B are block diagrams of, respectively, a CABAC encoder anda CABAC decoder providing both context coding mode and bypass codingmode;

FIG. 3 is a block diagram of a digital system;

FIG. 4 is a block diagram of a video encoder;

FIG. 5 is a block diagram of a video decoder;

FIGS. 6-11 are flow diagrams of methods; and

FIG. 12 is a block diagram of an illustrative digital system.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency.

As used herein, the term “picture” may refer to a frame or a field of aframe. A frame is a complete image captured during a known timeinterval. The Joint Collaborative Team on Video Coding (JCT-VC) of ITU-TWP3/16 and ISO/IEC JTC 1/SC 29/WG 11 is currently developing thenext-generation video coding standard referred to as High EfficiencyVideo Coding (HEVC). HEVC is expected to provide around 50% improvementin coding efficiency over the current standard, H.264/AVC, as well aslarger resolutions and higher frame rates. For convenience ofdescription, some embodiments of the invention are described herein inreference to HEVC and use terminology from HEVC. One of ordinary skillin the art will understand that embodiments of the invention are notlimited to HEVC.

In HEVC, a largest coding unit (LCU) is the base unit used forblock-based coding. A picture is divided into non-overlapping LCUs. Thatis, an LCU plays a similar role in coding as the macroblock ofH.264/AVC, but it may be larger, e.g., 32×32, 64×64, etc. An LCU may bepartitioned into coding units (CU). A CU is a block of pixels within anLCU and the CUs within an LCU may be of different sizes. Thepartitioning is a recursive quadtree partitioning. The quadtree is splitaccording to various criteria until a leaf is reached, which is referredto as the coding node or coding unit. The maximum hierarchical depth ofthe quadtree is determined by the size of the smallest CU (SCU)permitted. The coding node is the root node of two trees, a predictiontree and a transform tree. A prediction tree specifies the position andsize of prediction units (PU) for a coding unit. A transform treespecifies the position and size of transform units for a coding unit. Atransform unit may not be larger than a coding unit. In recentspecifications, the size of a square transform unit may be 4×4, 8×8,16×16, and 32×32 and the size of a non-square transform may be 16×4,4×16, 32×8, and 8×32. The sizes of the transforms units and predictionunits for a CU are determined by the video encoder during predictionbased on minimization of rate/distortion costs.

Various versions of HEVC are described in the following documents, whichare incorporated by reference herein: T. Wiegand, et al., “WD3: WorkingDraft 3 of High-Efficiency Video Coding,” JCTVC-E603, JointCollaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 andISO/IEC JTC1/SC29/WG11, Geneva, CH, Mar. 16-23, 2011 (“WD3”), B. Bross,et al., “WD4: Working Draft 4 of High-Efficiency Video Coding,”JCTVC-F803_d6, Joint Collaborative Team on Video Coding (JCT-VC) ofITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Torino, IT, Jul. 14-22, 2011(“WD4”), B. Bross. et al., “WD5: Working Draft 5 of High-EfficiencyVideo Coding,” JCTVC-G1103_d9, Joint Collaborative Team on Video Coding(JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Geneva, CH, Nov.21-30, 2011 (“WD5”), B. Bross, et al., “High Efficiency Video Coding(HEVC) Text Specification Draft 6,” JCTVC-H1003, Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG1, Geneva, CH, Nov. 21-30, 2011 (“HEVC Draft 6”), B. Bross,et al., “High Efficiency Video Coding (HEVC) Text Specification Draft7,” JCTVC-I1003_d0, Joint Collaborative Team on Video Coding (JCT-VC) ofITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG1, Geneva, CH, Apr. 17-May 7,2012 (“HEVC Draft 7”), B. Bross, et al., “High Efficiency Video Coding(HEVC) Text Specification Draft 8,” JCTVC-J1003_d7, Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG1, Stockholm, SE, Jul. 11-20, 2012 (“HEVC Draft 8”), and B.Bross, et al., “High Efficiency Video Coding (HEVC) Text SpecificationDraft 9,” JCTVC-K1003_v7, Joint Collaborative Team on Video Coding(JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG1, Shanghai, CN, Oct.10-19, 2012 (“HEVC Draft 9”). Each of these documents describes CABACcoding.

Some aspects of this disclosure have been presented to the JCT-VC in V.Sze and M. Budagavi, “Reduction in Context Coded Bins for ref_idx andcu_qp_delta”, JCTVC-I0204, Joint Collaborative Team on Video Coding(JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Geneva,Switzerland, Apr. 27-May 12, 2012, V. Sze, et al., “Bin Reduction forDelta QP Coding”, JCTVC-J0089, Joint Collaborative Team on Video Coding(JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Stockholm,Sweden, Jul. 11-20, 2012, V. Seregin, et al., “AHG5: Bypass Bins forReference Index Coding”, JCTVC-J0098, Joint Collaborative Team on VideoCoding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Stockholm,Sweden, Jul. 11-20, 2012, and M. Budagavi and V. Sze,“coeff_abs_level_remaining Maximum Codeword Length Reduction”,JCTVC-J0142, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-TSG16 WP3 and ISO/IEC JTC1/SC29/WG11, Stockholm, Sweden, Jul. 11-20,2012, which are incorporated by reference herein in their entirety.

Context-adaptive binary arithmetic coding (CABAC) is used toencode/decode syntax elements in the emerging HEVC standard. FIGS. 1Aand 1B are block diagrams illustrating the three key components of,respectively, CABAC encoding and CABAC decoding. Referring now to FIG.1A, a CABAC encoder includes a binarizer 100, a context modeler 102, anda bin encoder 104. The binarizer 100 converts syntax elements intostrings of one or more binary symbols referred to as bins. In general, asyntax element is an element of data produced by the video encodingprocess. For example, a syntax element may be a motion vectordifference, a prediction mode, a coefficient level, a flag, a referenceindex, etc. The syntax elements are defined by the video codingstandard, e.g., HEVC.

The binarization of a syntax element is also defined by the video codingstandard, i.e., the standard dictates the content of the binary symbolstring for each syntax element. That is, the coding standard defines abinarization scheme with unique mappings of syntax elements to sequencesof bins. Examples of binarization include unary coding, truncated unarycoding, exp-Golomb coding, and fixed length coding. Further, as part ofbinarization, a bin index (binIdx) is generated which indicates thelocation of the bin within the syntax element; the bin index inconjunction with the context selection logic indicates whether a bin maybe classified as a regular (context-coded) bin or an equal probability(bypass-coded) bin. Whether a particular bin is to be classified ascontext-coded or a bypass-coded is also defined by the video codingstandard. Context and bypass bins are explained in more detail below. Abin that is classified as context-coded is referred to as a context binherein and a bin that is classified as bypass-coded is referred as abypass bin herein.

The context modeler 102 selects a context model for a context bin. Thevideo coding standard defines the available context models, the initialvalues of the context models, and which context model(s) should be usedfor bins of each syntax element. A context model includes a state valueand a binary value of the most probable symbol MPS. The context modelsare updated throughout the coding process to track the probabilityestimations. That is, a bin is encoded based on the current state of thecontext model selected by the context modeler 102, and the context modelis then updated to reflect the state transition and the MPS after thebin is coded. This updating corresponds to the feedback loop labeled“context update” in FIG. 1A.

The bin encoder 104 performs binary arithmetic coding of a bin using thecontext model (probability) selected by the context modeler 102. Binaryarithmetic coding is based on the principle of recursive intervalsubdivision of an interval of width R. The current interval for eachrecursion, i.e., the internal state of the arithmetic coding, isrepresented by its lower bound L and its width (range) R. For each binto be encoded, the current interval is subdivided into two subintervals,an interval of width R_(LPS)=R*p_(LPS) and an interval of widthR_(MPS)=R−R_(LPS), where p_(LPS) is an estimate of the probability ofthe least probable symbol (LPS), and MPS is the most probable symbol,with a probability of 1−p_(LPS). The value of p_(LPS) is determinedusing the state value of the context model. Depending on whether the binis the LPS or MPS, the corresponding subinterval is selected as theinterval for the next bin.

The lower bound L and the range R are updated according to the lowerbound and range of the selected subinterval. A renormalization processis then executed to rescale the lower bound L and the range R if needed.The renormalization process iteratively scales the range R to a minimumvalue of 256 with successive left shifts by 1 and may take from zero to8 iterations depending on the value of the range R. In each iteration,the lower bound L is also scaled and a single output bit is generated tobe added to the encoded bit stream. The polarity of the output bit isdetermined by the value of the lower bound L at each iteration. However,in certain cases, the polarity of an output bit may need to be resolvedin subsequent iterations or in renormalization after coding one or moresubsequent bins, i.e., carry propagation may occur. Such bits arereferred to as outstanding bits. A count is kept of these outstandingbits and they are output when a future output bit resolves them to aknown value. Thus, 0 to 8 output bits may be generated duringrenormalization plus any outstanding bits may also be output. Therenormalization process corresponds to the feedback loop labeled“renormalization” in FIG. 1A.

The CABAC decoding process is the inverse of the encoding process andhas similar feedback loops. Referring now to FIG. 1B, a CABAC decoderincludes a bin decoder 112, a context modeler 110, and a de-binarizer114. The context modeler 110 selects a context model for the nextcontext bin to be decoded. As in the encoder, the context models areupdated throughout the decoding process to track the probabilityestimations. That is, a bin is decoded based on the current state of thecontext model selected by the context modeler 110, and the context modelis then updated to reflect the state transition and the MPS after thebin is decoded. This updating corresponds to the feedback loop labeled“context update” in FIG. 1B.

The bin decoder 112 performs binary arithmetic decoding of a bin usingthe context model selected by the context modeler 110. Binary arithmeticdecoding, like binary arithmetic encoding, is based on the principle ofrecursive interval subdivision of an interval of width (range) R. Theinternal state of the arithmetic decoding for each recursion isrepresented by the range R and an offset 0 used to select the correctsubinterval for a bin. A decoded bin is output at each recursion.

To decode a bin, the current interval is subdivided into twosubintervals, an interval of width R_(LPS)=R*p_(LPS) and an interval ofwidth R_(MPS)=R−R_(LPS), where p_(LPS) is an estimate of the probabilityof the least probable symbol (LPS), and MPS is the most probable symbol,with a probability of 1−p_(LPS). The value of p_(LPS) is determinedusing the state value of the context model. If the offset falls in thesubinterval R_(LPS), the bin is decoded as the LPS and the subintervalis selected as the interval for decoding the next bin; otherwise, thebin is decoded as the MPS and R_(MPS) is selected as the interval fordecoding the next bin.

The range R is updated to be the selected subinterval. A renormalizationprocess is then executed to rescale the range R and update the offset Oif needed. The renormalization process iteratively scales the range R toa minimum value of 256 with successive left shifts by 1. The number ofiterations needed depends on the value of the range R. In eachiteration, the offset 0 is also left shifted by 1 and the next bit inthe bit stream is shifted into the offset. The renormalization processcorresponds to the feedback loop labeled “range update” in FIG. 1B.

The de-binarizer 114 receives the decoded bins and operates to reversethe binarization of the binarizer 100 to reconstruct syntax elements.

As was previously mentioned, a bin may be a context bin or a bypass bin.Thus, the bin encoder and the bin decoder can operate in two modes:context coding mode and bypass coding mode. FIGS. 2A and 2B are blockdiagrams of, respectively, a CABAC encoder with a bin encoder providingboth modes and a CABAC decoder with a bin decoder providing both modes.In context coding mode, context bins are encoded/decoded according tothe full context modeling process. This mode enables high codingefficiency but the throughput is limited due to the feedback loops. Inbypass coding mode, the bypass bins have an assumed fixed probability of0.5, which means that 0 and 1 occur in equal probability. In this mode,the context modeling is skipped and thus the feedback loop involved inthe modeling. Thus several bypass coded bins can be coded in parallel.Furthermore, with the 0.5 probability, the range update in thearithmetic coding engine can be implemented with a simple shift, whichreduces the delay in the range update loop. The reduced delay in therange update loop reduces the critical path of the arithmeticencoder/decoder allowing bypass bins to be processed at a higherthroughput than context bins. However, the coding efficiency of bypassbins is lower than that of context bins.

Referring now to the CABAC encoder of FIG. 2A, the binarizer 200converts syntax elements into strings of one or more binary symbols. Thebinarizer 200 directs each bin to either the context coding 206 or thebypass coding 208 of the bin encoder 204 based on a bin type determinedby the context modeler 202. The binarizer also provides a bin index(binIdx) for each bin to the context modeler 202.

The context modeler 202 determines the bin type, i.e., context orbypass, for each bin. The order in which syntax elements should occur inthe compressed video bit stream is known, so the type of each syntaxelement to be encoded can be determined prior to encoding based on thetypes of previously encoded syntax elements. Further, as previouslymentioned, for each syntax element, the type (bypass or context) of eachbin in the syntax element is known. Given the type of the syntax elementbeing encoded and which bin in the syntax element is the next to bedecoded, the context modeler 202 can determine whether a bin is acontext bin or a bypass bin. The context modeler 202 provides the bintype to the multiplexor 210 and, although not specifically shown, to thebinarizer 200.

If a bin is a context bin, the context modeler 202 also selects acontext model for the bin to be used by the context coding 206. Thecontext coding 206 operates as previously described to encode eachcontext bin. The bypass coding 208 operates as previously described toencode each bypass bin. The bit values generated by the context coding206 and bypass coding 208 are provided the multiplexer 210. Themultiplexor 210 selects the output of the context coding 206 or thebypass coding 208 to be output into the compressed bit stream accordingto the bin type provided by the context modeler 202.

Referring now to the CABAC decoder of FIG. 2B, the bin decoder 220receives the compressed video bit stream and directs the bit stream tothe bypass coding 222 or the context coding 224 according to bin typesdetermined by the context modeler 228.

The context modeler 228 determines the bin type for each bin to bedecoded. As was previously explained, the order in which syntax elementsshould occur in the compressed video bit stream is known. Thus, the typeof each syntax element to be decoded can be determined prior to decodingbased on the types of previously decoded syntax elements. Further, foreach syntax element, the type (bypass or context) of each bin in thesyntax element is known. Given the type of the syntax element beingdecoded and which bin in the syntax element is the next to be decoded,the context modeler 228 can determine whether the next bin is a contextbin or a bypass bin. The context modeler 228 provides the bin type tothe multiplexor 226 and, although not specifically shown, to the bindecoder 220.

If a bin is a context bin, the context modeler 220 also selects acontext model to be used by the context coding 224 to decode the bin.The context coding 224 operates as previously described to decode eachcontext bin. The bypass coding 222 operates as previously described todecode each bypass bin. The bins generated by the context coding 224 andbypass coding 222 are provided the multiplexer 226. The multiplexor 226selects the output of the context coding 224 or the bypass coding 222 tobe provided to the de-binarizer 230 according to the bin type providedby the context modeler 228. The de-binarizer 230 receives decoded binsfor a syntax element from the bin decoder 220 and operates to reversethe binarization of the encoder to reconstruct the syntax elements.

Truncated unary coding is used to binarize several syntax elements inHEVC. Unary coding of a syntax element involves signaling a bin stringof length N+1, where the first N bins are 1 and the last bin is 0. Thedecoder searches for a 0 to determine when the syntax element iscomplete. Truncated unary coding of a syntax element generates one lessbin that unary coding by setting a maximum on the largest possible valueof the syntax element (cMax). When N+1<cMax, the signaling is the sameas unary coding (first N bins are 1 and last bin is 0). However, ifN+1>cMax, then all bins are 1. The decoder searches for a 0 up to cMaxbins to determine when the syntax element is complete. An example oftruncated unary coding where cMax=10 is shown in Table 1.

TABLE 1 Value Bin string 0 0 1 10 2 110 3 1110 4 11110 5 111110 61111110 7 11111110 8 111111110 9 1111111110 10 1111111111

Truncated unary binarization is specified in HEVC Draft 6 for syntaxelements such as the difference between a luma quantization parameter(qp) for a coding unit and the prediction of the parameter (referred toas cu_qp_delta in early versions of HEVC), reference picture indices(ref_idx_I0, ref_idx_I1, ref_idx_Ic), etc. For these syntax elements,all bins are context coded. When cMax is a large value, the number ofcontext coded bins can be prohibitively large. For example, forcu_qp_delta, cMax can have a value of 52, which means in the worst case,a maximum of 26 context coded bins are signaled per coding unit (CU).This translates to 104 context coded bins per LCU (assuming 4 CUs in anLCU). In another example, for the reference indices, cMax can have avalue of 15. Thus, in the worst case, a maximum of 32 context coded binsare signaled per prediction unit (PU) since up to two reference indicescan be signaled per PU. This translates to 240 context coded bins perLCU (assuming 8 PUs in an LCU). For the worst case, these two types ofsyntax elements account for over 30% of the context coded bins. It wouldbe desirable to avoid using truncated unary coding of syntax elementswhere the value of cMax is large and the resulting bins are contextcoded.

In HEVC, the bins of some syntax elements are all bypass coded. Due tothe particular binarization specified for some such syntax elements inHEVC Draft 7, the worst case number of bypass bins for a few of thesesyntax elements is quite large. For example, the level (value) of anon-zero transform coefficient is encoded as some combination of threelevel indicators (syntax elements) that indicate if the coefficientlevel is greater than 1 (coeff_abs_level_greater1_flag), greater than 2(coeff_abs_level_greater2_flag), and the remaining actual value(coeff_abs_level_remaining). Bypass coding is specified for the bins ofthe syntax element coeff_abs_level_remaining and the binarization ofthis syntax element is specified as a variable length code (VLC) with aunary coded prefix and fixed length suffix, the size of which depends onthe prefix and a parameter cParam that is adaptively updated after eachcoeff_abs_level_remaining syntax element is coded. The parameter cParammay range in value from 0 to 4, and controls the length of a fixedlength suffix of the codewords. The value of cParam starts at 0 for eachtransform unit and may be increased in value when sufficiently largecoefficient values occur in the transform unit. The particularcoefficient values that may cause the value of cParam to be increasedare defined in HEVC.

This VLC may be referred to as U-FLC123-L37 where the U denotes that theprefix is unary coded, FLC123 indicates that the length of the suffixincreases by one each time the prefix length increases by one, and L37indicates that the maximum codeword length is 37. In this VLC, values0-8 are unary coded and for values above 8, the codeword is constructedas follows: the first eight bits have the value 1, the remainder of thecodeword prefix and the codeword suffix are formed by EG(0) of((coeff_abs-Level-remaining>>cParam)−8), and the fixed length suffix ofcParam bits is formed by the binary value ofcoeff_abs-Level-remaining−((coeff_abs-Level-remaining>>cParam)*2^(cParam)).Table 2 shows this code for the case where cParam=0. Table 3 shows thiscode for the case where cParam=1. In Table 3, the character “c”indicates the fixed length portion of the suffix due to the value ofcParam. Note that the worst case length for this syntax element in Table2 is 37 bins and in table 3 is 36 bins, which would be encoded in thebit stream as, respectively, 37 bits and 36 bits. Bypass coded syntaxelements of this length adversely affects CABAC decoding throughput andincreases decoding complexity, especially for hardware architecturesthat use 32-bit processors and/or 32-bit memories.

TABLE 2 Prefix Suffix Total code Prefix code codeword Input Value Prefixcode (unary) length CodeNum length length 0 0 1 0 0 1 1 10 2 1 0 2 2 1103 2 0 3 3 1110 4 3 0 4 4 11110 5 4 0 5 5 111110 6 5 0 6 6 1111110 7 6 07 7 11111110 8 7 0 8 8 111111110 9 8 0 9  9~10 1111111110 10 9 1 1111~14 11111111110 11 10 2 13 15~22 111111111110 12 11 3 15 23~381111111111110 13 12 4 17 39~70 11111111111110 14 13 5 19  71~134111111111111110 15 14 6 21 135~262 1111111111111110 16 15 7 23 263~51811111111111111110 17 16 8 25  519~1030 111111111111111110 18 17 9 271031~2054 1111111111111111110 19 18 10 29 2055~4102 1111111111111111111020 19 11 31 4103~8198 111111111111111111110 21 20 12 33  8199~163901111111111111111111110 22 21 13 35 16391~32774 1111111111111111111111023 22 14 37

TABLE 3 Fixed Prefix Suffix Total length code code code Input ValueCodeword prefix Codeword suffix suffix length length length 0~1 0 c 1 12 2~3 10 c 2 1 3 4~5 110 c 3 1 4 6~7 1110 c 4 1 5 8~9 11110 c 5 1 610~11 111110 c 6 1 7 12~13 1111110 c 7 1 8 14~15 11111110 c 8 1 9 16~17111111110 c 9 1 10 18~21 1111111110 x c 10 2 12 22~29 11111111110 xx c11 3 14 30~45 111111111110 xxx c 12 4 16 46~77 1111111111110 xxxx c 13 518  78~141 11111111111110 xxxxx c 14 6 20 142~269 111111111111110 xxxxxxc 15 7 22 270~525 1111111111111110 xxxxxxx c 16 8 24  526~103711111111111111110 xxxxxxxx c 17 9 26 1038~2061 111111111111111110xxxxxxxxx c 18 10 28 2062~4109 1111111111111111110 xxxxxxxxxx c 19 11 304110~8205 11111111111111111110 xxxxxxxxxxx c 20 12 32  8206~16397111111111111111111110 xxxxxxxxxxxx c 21 13 34 16398~327811111111111111111111110 xxxxxxxxxxxxx c 22 14 36

Embodiments of the invention provide for CABAC coding with a reducednumber of context coded and/or bypass coded bins. In some embodiments,rather than using only truncated unary binarization for the syntaxelement representing the delta quantization parameter and context codingall of the resulting bins, a different binarization is used and onlypart of the resulting bins are context coded, thus reducing the worstcase number of context coded bins for this syntax element. In someembodiments, a different binarization is used for the syntax elementrepresenting the remaining actual value of a transform coefficient(referred to as coeff_abs_level_remaining herein) that restricts themaximum codeword length of this syntax element to 32 bits or less, thusreducing the number of bypass coded bins for this syntax element.

FIG. 3 shows a block diagram of a digital system that includes a sourcedigital system 300 that transmits encoded video sequences to adestination digital system 302 via a communication channel 316. Thesource digital system 300 includes a video capture component 304, avideo encoder component 306, and a transmitter component 308. The videocapture component 304 is configured to provide a video sequence to beencoded by the video encoder component 306. The video capture component304 may be, for example, a video camera, a video archive, or a videofeed from a video content provider. In some embodiments, the videocapture component 304 may generate computer graphics as the videosequence, or a combination of live video, archived video, and/orcomputer-generated video.

The video encoder component 306 receives a video sequence from the videocapture component 304 and encodes it for transmission by the transmittercomponent 308. The video encoder component 306 receives the videosequence from the video capture component 304 as a sequence of pictures,divides the pictures into largest coding units (LCUs), and encodes thevideo data in the LCUs. The video encoder component 306 may beconfigured to perform CABAC encoding of delta quantization parametersyntax elements and/or transform coefficient remaining value syntaxelements during the encoding process as described herein. An embodimentof the video encoder component 306 is described in more detail herein inreference to FIG. 4.

The transmitter component 308 transmits the encoded video data to thedestination digital system 302 via the communication channel 316. Thecommunication channel 316 may be any communication medium, orcombination of communication media suitable for transmission of theencoded video sequence, such as, for example, wired or wirelesscommunication media, a local area network, or a wide area network.

The destination digital system 302 includes a receiver component 310, avideo decoder component 312 and a display component 314. The receivercomponent 310 receives the encoded video data from the source digitalsystem 300 via the communication channel 316 and provides the encodedvideo data to the video decoder component 312 for decoding. The videodecoder component 312 reverses the encoding process performed by thevideo encoder component 306 to reconstruct the LCUs of the videosequence. The video decoder component 312 may be configured to performCABAC decoding of delta quantization parameter syntax elements and/ortransform coefficient remaining value syntax elements during thedecoding process as described herein. An embodiment of the video decodercomponent 312 is described in more detail below in reference to FIG. 5.

The reconstructed video sequence is displayed on the display component314. The display component 314 may be any suitable display device suchas, for example, a plasma display, a liquid crystal display (LCD), alight emitting diode (LED) display, etc.

In some embodiments, the source digital system 300 may also include areceiver component and a video decoder component and/or the destinationdigital system 302 may include a transmitter component and a videoencoder component for transmission of video sequences both directionsfor video steaming, video broadcasting, and video telephony. Further,the video encoder component 306 and the video decoder component 312 mayperform encoding and decoding in accordance with one or more videocompression standards. The video encoder component 306 and the videodecoder component 312 may be implemented in any suitable combination ofsoftware, firmware, and hardware, such as, for example, one or moredigital signal processors (DSPs), microprocessors, discrete logic,application specific integrated circuits (ASICs), field-programmablegate arrays (FPGAs), etc.

FIG. 4 is a block diagram of the LCU processing portion of an examplevideo encoder. A coding control component (not shown) sequences thevarious operations of the LCU processing, i.e., the coding controlcomponent runs the main control loop for video encoding. The codingcontrol component receives a digital video sequence and performs anyprocessing on the input video sequence that is to be done at the picturelevel, such as determining the coding type (I, P, or B) of a picturebased on the high level coding structure, e.g., IPPP, IBBP,hierarchical-B, and dividing a picture into LCUs for further processing.

In addition, for pipelined architectures in which multiple LCUs may beprocessed concurrently in different components of the LCU processing,the coding control component controls the processing of the LCUs byvarious components of the LCU processing in a pipeline fashion. Forexample, in many embedded systems supporting video processing, there maybe one master processor and one or more slave processing modules, e.g.,hardware accelerators. The master processor operates as the codingcontrol component and runs the main control loop for video encoding, andthe slave processing modules are employed to off load certaincompute-intensive tasks of video encoding such as motion estimation,motion compensation, intra prediction mode estimation, transformationand quantization, entropy coding, and loop filtering. The slaveprocessing modules are controlled in a pipeline fashion by the masterprocessor such that the slave processing modules operate on differentLCUs of a picture at any given time. That is, the slave processingmodules are executed in parallel, each processing its respective LCUwhile data movement from one processor to another is serial.

The LCU processing receives LCUs 400 of the input video sequence fromthe coding control component and encodes the LCUs 400 under the controlof the coding control component to generate the compressed video stream.The LCUs 400 in each picture are processed in row order. The LCUs 400from the coding control component are provided as one input of a motionestimation component (ME) 420, as one input of an intra-predictionestimation component (IPE) 424, and to a positive input of a combiner402 (e.g., adder or subtractor or the like). Further, although notspecifically shown, the prediction mode of each picture as selected bythe coding control component is provided to a mode decision component428 and the entropy coding component 436.

The storage component 418 provides reference data to the motionestimation component 420 and to the motion compensation component 422.The reference data may include one or more previously encoded anddecoded pictures, i.e., reference pictures.

The motion estimation component 420 provides motion data information tothe motion compensation component 422 and the entropy coding component436. More specifically, the motion estimation component 420 performstests on CUs in an LCU based on multiple inter-prediction modes (e.g.,skip mode, merge mode, and normal or direct inter-prediction),prediction unit sizes, and transform unit sizes using reference picturedata from storage 418 to choose the best CU partitioning, predictionunit/transform unit partitioning, inter-prediction modes, motionvectors, etc. based on coding cost, e.g., a rate distortion coding cost.To perform the tests, the motion estimation component 420 may divide anLCU into CUs according to the maximum hierarchical depth of thequadtree, and divide each CU into prediction units according to the unitsizes of the inter-prediction modes and into transform units accordingto the transform unit sizes, and calculate the coding costs for eachprediction unit size, prediction mode, and transform unit size for eachCU. The motion estimation component 420 provides the motion vector (MV)or vectors and the prediction mode for each prediction unit in theselected CU partitioning to the motion compensation component (MC) 422.

The motion compensation component 422 receives the selectedinter-prediction mode and mode-related information from the motionestimation component 420 and generates the inter-predicted CUs. Theinter-predicted CUs are provided to the mode decision component 428along with the selected inter-prediction modes for the inter-predictedprediction units and corresponding transform unit sizes for the selectedpartitioning. The coding costs of the inter-predicted CUs are alsoprovided to the mode decision component 428.

The intra-prediction estimation component 424 (IPE) performsintra-prediction estimation in which tests on CUs in an LCU based onmultiple intra-prediction modes, prediction unit sizes, and transformunit sizes are performed using reconstructed data from previouslyencoded neighboring CUs stored in a buffer (not shown) to choose thebest CU partitioning, prediction unit/transform unit partitioning, andintra-prediction modes based on coding cost, e.g., a rate distortioncoding cost. To perform the tests, the intra-prediction estimationcomponent 424 may divide an LCU into CUs according to the maximumhierarchical depth of the quadtree, and divide each CU into predictionunits according to the unit sizes of the intra-prediction modes and intotransform units according to the transform unit sizes, and calculate thecoding costs for each prediction unit size, prediction mode, andtransform unit size for each prediction unit. The intra-predictionestimation component 424 provides the selected intra-prediction modesfor the prediction units, and the corresponding transform unit sizes forthe selected CU partitioning to the intra-prediction component (IP) 426.The coding costs of the intra-predicted CUs are also provided to theintra-prediction component 426.

The intra-prediction component 426 (IP) receives intra-predictioninformation, e.g., the selected mode or modes for the predictionunit(s), the prediction unit size, etc., from the intra-predictionestimation component 424 and generates the intra-predicted CUs. Theintra-predicted CUs are provided to the mode decision component 428along with the selected intra-prediction modes for the intra-predictedPUs and corresponding transform unit sizes for the selectedpartitioning. The coding costs of the intra-predicted CUs are alsoprovided to the mode decision component 428.

The mode decision component 428 selects between intra-prediction of a CUand inter-prediction of a CU based on the intra-prediction coding costof the CU from the intra-prediction component 426, the inter-predictioncoding cost of the CU from the motion compensation component 422, andthe picture prediction mode provided by the coding control component.Based on the decision as to whether a CU is to be intra- or inter-coded,the intra-predicted prediction units or inter-predicted prediction unitsare selected. The selected partitioning with corresponding modes andother mode related prediction data (if any) such as motion vector(s) andreference picture index (indices), are provided to the entropy codingcomponent 436.

The output of the mode decision component 428, i.e., the predictedprediction units, is provided to a negative input of the combiner 402and to the combiner 438. The associated transform unit size is alsoprovided to the transform component 404. The combiner 402 subtracts apredicted prediction unit from the original prediction unit. Eachresulting residual prediction unit is a set of pixel difference valuesthat quantify differences between pixel values of the originalprediction unit and the predicted prediction unit. The residual blocksof all the prediction units of a CU form a residual CU for furtherprocessing.

The transform component 404 performs block transforms on the residualCUs to convert the residual pixel values to transform coefficients andprovides the transform coefficients to a quantize component 406. Morespecifically, the transform component 404 receives the transform unitsizes for the residual CU and applies transforms of the specified sizesto the CU to generate transform coefficients. Further, the quantizecomponent 406 quantizes the transform coefficients based on quantizationparameters (QPs) and quantization matrices provided by the codingcontrol component and the transform sizes and provides the quantizedtransform coefficients to the entropy coding component 436 for coding inthe bit stream.

The entropy coding component 436 entropy encodes the relevant data,i.e., syntax elements, output by the various encoding components and thecoding control component using context-adaptive binary arithmetic coding(CABAC) to generate the compressed video bit stream. Among the syntaxelements that are encoded are picture parameter sets, flags indicatingthe partitioning of an LCU, the prediction modes for the CUs, thequantized transform coefficients for the CUs, and a delta quantizationparameter for each CU. The entropy coding component 436 encodes thesyntax elements using CABAC encoding. The entropy coding component 436may entropy encode the delta quantization parameter syntax elementsand/or the transform coefficient remaining actual value syntax elementsaccording to techniques described herein.

The LCU processing component 442 includes an embedded decoder. As anycompliant decoder is expected to reconstruct an image from a compressedbit stream, the embedded decoder provides the same utility to the videoencoder. Knowledge of the reconstructed input allows the video encoderto transmit the appropriate residual energy to compose subsequentpictures.

The quantized transform coefficients for each CU are provided to aninverse quantize component (IQ) 412, which outputs a reconstructedversion of the transform result from the transform component 404. Thedequantized transform coefficients are provided to the inverse transformcomponent (IDCT) 414, which outputs estimated residual informationrepresenting a reconstructed version of a residual CU. The inversetransform component 414 receives the transform unit size used togenerate the transform coefficients and applies inverse transform(s) ofthe specified size to the transform coefficients to reconstruct theresidual values. The reconstructed residual CU is provided to thecombiner 438.

The combiner 438 adds the original predicted CU to the residual CU togenerate a reconstructed CU, which becomes part of reconstructed picturedata. The reconstructed picture data is stored in a buffer (not shown)for use by the intra-prediction estimation component 424.

Various in-loop filters may be applied to the reconstructed picture datato improve the quality of the reference picture data used forencoding/decoding of subsequent pictures. The in-loop filters mayinclude a deblocking filter 430, a sample adaptive offset filter (SAO)432, and an adaptive loop filter (ALF) 434. The in-loop filters 430,432, 434 are applied to each reconstructed LCU in the picture and thefinal filtered reference picture data is provided to the storagecomponent 418. In some embodiments, the ALF component 434 is notpresent.

FIG. 5 is a block diagram of an example video decoder. The entropydecoding component 500 receives an entropy encoded (compressed) videobit stream and reverses the entropy encoding using CABAC decoding torecover the encoded syntax elements, e.g., CU, prediction unit, andtransform unit structures of LCUs, quantized transform coefficients forCUs, a delta quantization parameter for each CU, motion vectors,prediction modes, in-loop filter parameters, etc. The entropy decodingcomponent 500 decodes the syntax elements using CABAC decoding. Theentropy decoding component 500 may entropy decode the delta quantizationparameter syntax elements and/or the transform coefficient remainingvalue syntax elements according to techniques described herein. Thedecoded syntax elements are passed to the various components of thedecoder as needed. For example, decoded prediction modes are provided tothe intra-prediction component (IP) 514 or motion compensation component(MC) 510. If the decoded prediction mode is an inter-prediction mode,the entropy decoder 500 reconstructs the motion vector(s) as needed andprovides the motion vector(s) to the motion compensation component 510.

The inverse quantize component (IQ) 502 de-quantizes the quantizedtransform coefficients of the CUs. The inverse transform component 504transforms the frequency domain data from the inverse quantize component502 back to the residual CUs. That is, the inverse transform component504 applies an inverse unit transform, i.e., the inverse of the unittransform used for encoding, to the de-quantized residual coefficientsto produce reconstructed residual values of the CUs.

A residual CU supplies one input of the addition component 506. Theother input of the addition component 506 comes from the mode switch508. When an inter-prediction mode is signaled in the encoded videostream, the mode switch 508 selects predicted PUs from the motioncompensation component 510 and when an intra-prediction mode issignaled, the mode switch selects predicted PUs from theintra-prediction component 514.

The motion compensation component 510 receives reference data from thestorage component 512 and applies the motion compensation computed bythe encoder and transmitted in the encoded video bit stream to thereference data to generate a predicted PU. That is, the motioncompensation component 510 uses the motion vector(s) from the entropydecoder 500 and the reference data to generate a predicted PU.

The intra-prediction component 514 receives reconstructed samples frompreviously reconstructed PUs of a current picture from the storagecomponent 512 and performs the intra-prediction computed by the encoderas signaled by an intra-prediction mode transmitted in the encoded videobit stream using the reconstructed samples as needed to generate apredicted PU.

The addition component 506 generates a reconstructed CU by adding thepredicted PUs selected by the mode switch 508 and the residual CU. Theoutput of the addition component 506, i.e., the reconstructed CUs, isstored in the storage component 512 for use by the intra-predictioncomponent 514.

In-loop filters may be applied to reconstructed picture data to improvethe quality of the decoded pictures and the quality of the referencepicture data used for decoding of subsequent pictures. The in-loopfilters are the same as those of the encoder, i.e., a deblocking filter516, a sample adaptive offset filter (SAO) 518, and an adaptive loopfilter (ALF) 520. The in-loop filters may be applied on an LCU-by-LCUbasis and the final filtered reference picture data is provided to thestorage component 512. In some embodiments, the ALF component 520 is notpresent.

FIG. 6 is a flow diagram of a method for CABAC encoding of a deltaquantization parameter syntax element using a variable length code (VLC)in which the value of the syntax element is binarized using acombination of truncated unary (TU) and kth order exponential Golomb(exp-Golomb) coding. More specifically, a prefix of the syntax elementvalue is binarized using TU coding with a small value of cMax and asuffix is binarized using kth order exp-Golomb coding (EGk). Further,the bins of the TU coded prefix are context-coded and the bins of theEGk coded suffix are bypass coded. Any suitable values of cMax and k maybe used. In some embodiments, cMax=4 and k=0. In some embodiments,cMax=5 and k=0.

TU coding is previously explained herein. Exp-Golomb codes are indexedby a non-negative integer value k, referred to as the order of the code.Furthermore, the output of the particular EGk coding used is a threepart code word that includes a unary prefix of one bits, a binarysuffix, and a separator between the prefix and suffix that is a singlezero bit. More specifically, to encode a non-negative integer n using anexp-Golomb code of order k, the number of one bits q in the prefix ofthe codeword may be calculated as shown in Eq. (1) and the value r ofthe suffix may be calculated as shown in Eq. (2). The length of thesuffix is q+k. The codeword for n consists of a prefix q one bits, thesingle zero bit separator, and a suffix of q+k bits containing thebinary representation of r. The codeword may also be obtained directlyas the binary representation of the sum n+2^(k), zero-extended by qbits. Further, the length of the codeword for n is 2q+k+1.q=log₂((n+2^(k))>>k)  (1)r=n+2^(k)−2^(q+k)  (2)Exp-Golomb coding of integers m with negative and non-negative valuescan be carried out by mapping the negative and non-negative values of minto positive values n. An example mapping is as follows:

mapping from m to n:

-   -   if(m<=0) n=−2*m    -   else n=2*m−1

mapping from n to m:

-   -   if (n & 0×1) m=(n+1)/2

else m=−n/2.

Referring again to FIG. 6, in this method, the variable i is a bincounter and the variable N is the absolute value of a delta quantizationparameter (delta qp) syntax element. Initially, the value of the bincounter i is set to 0. In this method, for values of N greater than orequal to cMax, cMax bins with a value of 1 are context coded into thecompressed bit stream followed by bypass coded bins corresponding to theEGk codeword for N−cMax. For values of N less than cMax and greater than0, N bins with a value of 1 are context coded into the compressed bitstream followed a context coded bin with a value of 0. If N=0, a singlebin with a value of 0 is context coded into the compressed bit stream.If the value of delta qp is not zero, a single bin indicating the signof delta qp is bypass coded into the compressed bit stream after thevalue. Table 4 shows the encoding of input values 0-10 according to thismethod assuming cMax=4 and k=0. Table 5 shows the encoding of inputvalues 0-26 according to this method assuming cMax=5 and k=0. Note thatwith cMax=5 and k=0, the worst case number of context coded bins is 5and the worst case number of total bins is 15.

Table 5 assumes a range of −26 to 25 for the value of delta qp. Thevalue range for this syntax element changes based on the bit depth ofthe video sequence. For 8-bit video, the range is −26 to 25, for 10-bitvideo, the range is −32 to 31, and for 12-bit video, the range is −38 to37.

TABLE 4 Bin string Bin string Value (truncated unary) (0^(th) orderExp-Golomb) 0 0 1 10 2 110 3 1110 4 1111 0 5 1111 100 6 1111 101 7 111111000 8 1111 11001 9 1111 11010 10 1111 11011

TABLE 5 Bin string Bin string Value (TU with cMax = 5) (EG with k = 0) 00 1 10 2 110 3 1110 4 11110 5 11111 0 6 11111 100 7 11111 101 8 1111111000 . . . . . . . . . 26  11111 111100110

FIG. 7 is a flow diagram of a method for CABAC decoding of a deltaquantization parameter syntax element encoded by the method of FIG. 6.In this method, the variable i is a bin counter, the value of which isinitially 0. Context coded bins are decoded until either cMax bins withthe value of 1 are decoded or a bin with a value of 0 is decoded. If abin with the value of 0 is decoded before cMax bins are decoded, thevalue of delta qp is set to b, which is the number of decoded bins witha value of 1. If cMax bins with a value of 1 are decoded, then thebypass coded bins of the EGk coded suffix are decoded and the value ofdelta qp is set to the sum of cMax and the suffix. After the value ofdelta qp is decoded, if the value is not zero, then a bypass coded binindicating the sign of delta qp is decoded and applied to the value.

FIGS. 8 and 9, and Tables 8-20, present methods for CABAC coding anddecoding of the syntax element representing the remaining actual valueof a transform coefficient that limit the worst case (maximum) size ofthe binarization of this syntax element to 32 bins. For examplepurposes, this syntax element is referred to herein by the name used inHEVC, i.e., coeff_abs_level_remaining. As previously explained, in theprior art VLC used for binarization of coeff_abs_level_remaining, theworst case codeword length is 37 bins when cParam=0. Tables 8-20illustrate embodiments of VLCs that restrict the maximum codeword sizeto 32 bins.

Referring first to Tables 8-18, in the prior art VLC for binarization ofcoeff_abs_level_remaining, when cParam=0, syntax element values lessthan 9 are unary coded only, resulting in a worst case codeword lengthof 37 (see Table 2). As illustrated in Tables 8-18, the VLC can be movedup such that the suffix coding starts for syntax element values smallerthan 9, resulting in a worst case codeword length of 32 or less. Tables8-12 illustrate a VLC in which the suffix coding starts for syntaxelements larger than 3. This VLC is referred to as U-FLC123-L32, wherethe U denotes that the prefix is unary coded, FLC123 denotes that thecodeword suffix length increments by 1 for each increase in prefixcodeword length, and L32 indicates the maximum codeword length is 32bits. In this VLC, values 0-3 are unary coded and for values above 3 thecodeword is constructed as follows: the first three bits have the value1, the remainder of the codeword prefix and the codeword suffix areformed by EG(0) of ((coeff_abs-Level-remaining>>cParam)−3), and thefixed length suffix of cParam bits is formed by the binary value ofcoeff_abs-Level-remaining−((coeff_abs-Level-remaining>>cParam)*2^(cParam)).Table 8 shows the VLC for the case where cParam=0, Table 9 shows the VLCfor the case where cParam=1, Table 10 shows the VLC for the case wherecParam=2, Table 11 shows the VLC for the case where cParam=3, and Table12 shows the VLC for the case where cParam=4.

Tables 8-18 (and other tables herein) use a notation that allows acompact representation of the full code. The range of possible values ofcoeff_abs_level_remaining is very large. Rather than listing theindividual codewords for each possible syntax element value, lines in atable may represent several codewords. The characters “x” and “c” areused to indicate the number of bits, respectively, in the codewordsuffix and the fixed length suffix for ranges of input values. Further,the number of “c” bits depends on the value of cParam. The actual valuesof these bits will differ for each input value in the range. Forexample, Table 6 illustrates the expansion of a line in Table 8, andTable 7 illustrates the expansion of a line in Table 11.

TABLE 6 Fixed Prefix Suffix Total Input Codeword Codeword length codecode code Value prefix suffix suffix length length length 6~9 111110 xx6 2 8 Actual table 6 111110 00 7 111110 01 8 111110 10 9 111110 11

TABLE 7 Fixed Prefix Suffix Total Input Codeword Codeword length codecode code Value prefix suffix suffix length length length 32~47 11110 xccc 5 4 9 Actual table 32 11110 0 000 33 11110 0 001 34 11110 0 010 3511110 0 011 36 11110 0 100 37 11110 0 101 38 11110 0 110 39 11110 0 11140 11110 1 000 41 11110 1 001 42 11110 1 010 43 11110 1 011 44 11110 1100 45 11110 1 101 46 11110 1 110 47 11110 1 111

TABLE 8 Fixed Prefix Suffix Total len code code code Input ValueCodeword prefix Codeword suffix suffix len len len 0 0 1 0 1 1 10 2 0 22 110 3 0 3 3 1110 4 0 4 4~5 11110 x 5 1 6 6~9 111110 xx 6 2 8 10~171111110 xxx 7 3 10 18~33 11111110 xxxx 8 4 12 34~65 111111110 xxxxx 9 514  66~129 1111111110 xxxxxx 10 6 16 130~257 11111111110 xxxxxxx 11 7 18258~513 111111111110 xxxxxxxx 12 8 20  514~1025 1111111111110 xxxxxxxxx13 9 22 1026~2049 11111111111110 xxxxxxxxxx 14 10 24 2050~4097111111111111110 xxxxxxxxxxx 15 11 26 4098~8193 1111111111111110xxxxxxxxxxxx 16 12 28  8194~16385 11111111111111110 xxxxxxxxxxxxx 17 1330 16386~32769 111111111111111110 xxxxxxxxxxxxxx 18 14 32

TABLE 9 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length 0~1 0 c 1 1 22~3 10 c 2 1 4~5 110 c 3 1 4 6~7 1110 c 4 1 5  8~11 11110 x c 5 2 712~19 111110 xx c 6 3 9 20~35 1111110 xxx c 7 4 11 36~67 11111110 xxxx c8 5 13  68~131 111111110 xxxxx c 9 6 15 132~259 1111111110 xxxxxx c 10 717 260~515 11111111110 xxxxxxx c 11 8 19  516~1027 111111111110 xxxxxxxxc 12 9 21 1028~2051 1111111111110 xxxxxxxxx c 13 10 23 2052~409911111111111110 xxxxxxxxxx c 14 11 25 4100~8195 111111111111110xxxxxxxxxxx c 15 12 27  8196~16387 1111111111111110 xxxxxxxxxxxx c 16 1329 16388~32771 1111111111111110 xxxxxxxxxxxx c 17 14 31

TABLE 10 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length 0~3 0 cc 1 2 34~7 10 cc 2 2 4  8~11 110 cc 3 2 5 12~15 1110 cc 4 2 6 16~23 11110 x cc5 3 8 24~39 111110 xx cc 6 4 10 40~71 1111110 xxx cc 7 5 12  72~13511111110 xxxx cc 8 6 14 136~263 111111110 xxxxx cc 9 7 16 264~5191111111110 xxxxxx cc 10 8 18  520~1031 11111111110 xxxxxxx cc 11 9 201032~2055 111111111110 xxxxxxxx cc 12 10 22 2056~4103 1111111111110xxxxxxxxx cc 13 11 24 4104~8199 11111111111110 xxxxxxxxxx cc 14 12 26 8200~16391 111111111111110 xxxxxxxxxxx cc 15 13 28 16392~327751111111111111110 xxxxxxxxxxxx cc 16 14 30

TABLE 11 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length 0~7 0 ccc 1 3 4 8~15 10 ccc 2 3 5 16~23 110 ccc 3 3 6 24~31 1110 ccc 4 3 7 32~47 11110x ccc 5 4 9 48~79 111110 xx ccc 6 5 11  80~143 1111110 xxx ccc 7 6 13144~271 11111110 xxxx ccc 8 7 15 272~527 111111110 xxxxx ccc 9 8 17 528~1039 1111111110 xxxxxx ccc 10 9 19 1040~2063 11111111110 xxxxxxxccc 11 10 21 2064~4111 111111111110 xxxxxxxx ccc 12 11 23 4112~82071111111111110 xxxxxxxxx ccc 13 12 25  8208~16399 11111111111110xxxxxxxxxx ccc 14 13 27 16400~32783 111111111111110 xxxxxxxxxxx ccc 1514 29

TABLE 12 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length  0~15 0 cccc 14 5 16~31 10 cccc 2 4 6 32~47 110 cccc 3 4 7 48~63 1110 cccc 4 4 8 64~9511110 x cccc 5 5 10  96~159 111110 xx cccc 6 6 12 160~287 1111110 xxxcccc 7 7 14 288~543 11111110 xxxx cccc 8 8 16  544~1055 111111110 xxxxxcccc 9 9 18 1056~2079 1111111110 xxxxxx cccc 10 10 20 2080~412711111111110 xxxxxxx cccc 11 11 22 4128~8223 111111111110 xxxxxxxx cccc12 12 24  8224~16415 1111111111110 xxxxxxxxx cccc 13 13 26 16416~3279911111111111110 xxxxxxxxxx cccc 14 14 28

Tables 13-17 illustrate a VLC in which the suffix coding starts forsyntax elements larger than 3 and truncated unary coding is used for thecodeword prefix. This VLC is referred to as TU-FLC123-L31, where the TUdenotes that the prefix is truncated unary coded, FLC123 denotes thatthe length of the codeword suffix increments by 1 for each increase inprefix codeword length, and L31 indicates the maximum codeword length is31 bits. Table 13-17 are modified versions of Tables 8-12. Since themaximum value of coeff_abs-level-remaining that can be coded in HEVC is32768, there will be no VLC entries after the last rows of Tables 8-12.As a result of which the prefix for the last rows of Tables 8-12 can betruncated by removing the zero bit in prefix as shown in the last rowsof Tables 13-17, respectively. Tables 13-17 show, respectively, the VLCfor the cases where cParam=0, 1, 2, 3, 4.

Tables 13-17 are examples of the use of truncated unary prefix coding.Other table sets can be created by varying the point at which the suffixcoding starts for cParam=0. For example, if suffix coding starts atvalues larger than 4 and truncated unary coding is used for the codewordprefix, a TU-FLC123-L32 codeword results as shown in Table 18 forcParam=0. One of ordinary skill in the art will understand this VLC forlarger values of cParam, and will understand that as cParam increases,the maximum codeword length may differ from that for cParam=0, but willnot exceed 32 bits.

TABLE 13 Fixed Prefix Suffix Total len code code code Input ValueCodeword prefix Codeword suffix suffix len len len 0 0 1 0 1 1 10 2 0 22 110 3 0 3 3 1110 4 0 4 4~5 11110 x 5 1 6 6~9 111110 xx 6 2 8 10~171111110 xxx 7 3 10 18~33 11111110 xxxx 8 4 12 34~65 111111110 xxxxx 9 514  66~129 1111111110 xxxxxx 10 6 16 130~257 11111111110 xxxxxxx 11 7 18258~513 111111111110 xxxxxxxx 12 8 20  514~1025 1111111111110 xxxxxxxxx13 9 22 1026~2049 11111111111110 xxxxxxxxxx 14 10 24 2050~4097111111111111110 xxxxxxxxxxx 15 11 26 4098~8193 1111111111111110xxxxxxxxxxxx 16 12 28  8194~16385 11111111111111110 xxxxxxxxxxxxx 17 1330 16386~32769 11111111111111111 xxxxxxxxxxxxxx 17 14 31

TABLE 14 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length 0~1 0 c 1 1 22~3 10 c 2 1 4~5 110 c 3 1 4 6~7 1110 c 4 1 5  8~11 11110 x c 5 2 712~19 111110 xx c 6 3 9 20~35 1111110 xxx c 7 4 11 36~67 11111110 xxxx c8 5 13  68~131 111111110 xxxxx c 9 6 15 132~259 1111111110 xxxxxx c 10 717 260~515 11111111110 xxxxxxx c 11 8 19  516~1027 111111111110 xxxxxxxxc 12 9 21 1028~2051 1111111111110 xxxxxxxxx c 13 10 23 2052~409911111111111110 xxxxxxxxxx c 14 11 25 4100~8195 111111111111110xxxxxxxxxxx c 15 12 27  8196~16387 1111111111111110 xxxxxxxxxxxx c 16 1329 16388~32771 1111111111111111 xxxxxxxxxxxxx c 16 14 30

TABLE 15 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length 0~3 0 cc 1 2 34~7 10 cc 2 2 4  8~11 110 cc 3 2 5 12~15 1110 cc 4 2 6 16~23 11110 x cc5 3 8 24~39 111110 xx cc 6 4 10 40~71 1111110 xxx cc 7 5 12  72~13511111110 xxxx cc 8 6 14 136~263 111111110 xxxxx cc 9 7 16 264~5191111111110 xxxxxx cc 10 8 18  520~1031 11111111110 xxxxxxx cc 11 9 201032~2055 111111111110 xxxxxxxx cc 12 10 22 2056~4103 1111111111110xxxxxxxxx cc 13 11 24 4104~8199 11111111111110 xxxxxxxxxx cc 14 12 26 8200~16391 11111111111111 xxxxxxxxxxx cc 14 13 27 16392~327751111111111111110 xxxxxxxxxxxx cc 16 14 30

TABLE 16 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length 0~7 0 ccc 1 3 4 8~15 10 ccc 2 3 5 16~23 110 ccc 3 3 6 24~31 1110 ccc 4 3 7 32~47 11110x ccc 5 4 9 48~79 111110 xx ccc 6 5 11  80~143 1111110 xxx ccc 7 6 13144~271 11111110 xxxx ccc 8 7 15 272~527 111111110 xxxxx ccc 9 8 17 528~1039 1111111110 xxxxxx ccc 10 9 19 1040~2063 11111111110 xxxxxxxccc 11 10 21 2064~4111 111111111110 xxxxxxxx ccc 12 11 23 4112~82071111111111110 xxxxxxxxx ccc 13 12 25  8208~16399 11111111111110xxxxxxxxxx ccc 14 13 27 16400~32783 11111111111111 xxxxxxxxxxx ccc 14 1428

TABLE 17 Fixed Prefix Suffix Total Codeword length code code code InputValue Codeword prefix suffix suffix length length length  0~15 0 cccc 14 5 16~31 10 cccc 2 4 6 32~47 110 cccc 3 4 7 48~63 1110 cccc 4 4 8 64~9511110 x cccc 5 5 10  96~159 111110 xx cccc 6 6 12 160~287 1111110 xxxcccc 7 7 14 288~543 11111110 xxxx cccc 8 8 16  544~1055 111111110 xxxxxcccc 9 9 18 1056~2079 1111111110 xxxxxx cccc 10 10 20 2080~412711111111110 xxxxxxx cccc 11 11 22 4128~8223 111111111110 xxxxxxxx cccc12 12 24  8224~16415 1111111111110 xxxxxxxxx cccc 13 13 26 16416~327991111111111111 xxxxxxxxxx cccc 13 14 27

TABLE 18 Prefix Suffix Total code code code Input Value Codeword prefixCodeword suffix length length length 0 0 1 0 1 1 10 2 0 2 2 110 3 0 3 31110 4 0 4 4 11110 5 0 5 5~6 111110 x 6 1 7  7~10 1111110 xx 7 2 9 11~1811111110 xxx 8 3 11 19~34 111111110 xxxx 9 4 13 35~66 1111111110 xxxxx10 5 15  67~130 11111111110 xxxxxx 11 6 17 131~258 111111111110 xxxxxxx12 7 19 259~514 1111111111110 xxxxxxxx 13 8 21  515~1026 11111111111110xxxxxxxxx 14 9 23 1027~2050 111111111111110 xxxxxxxxxx 15 10 252051~4098 1111111111111110 xxxxxxxxxxx 16 11 27 4099~819411111111111111110 xxxxxxxxxxxx 17 12 29  8195~16386 111111111111111110xxxxxxxxxxxxx 18 13 31 16387~32770 111111111111111111 xxxxxxxxxxxxxx 1814 32

Tables 19 and 20 illustrate a VLC in which escape coding is used toreduce maximum codeword length to 32. This VLC is the same as that ofthe prior art VLC (see Table 2) except that escape coding is used toforce the codeword suffix to be 15 bits for all values above a selectedvalue. The codeword suffix is coded with 15 bits because the maximumvalue of coeff_abs-Level-remaining that can be coded in HEVC is 32768.The value at which escape coding starts is controlled by the length ofthe prefix at which escape coding starts. Table 19 and 20 illustrateexamples of escape coding which starts when the prefix length is 17bits. The corresponding value of coeff_abs-level-remaining at whichescape coding will start is 263 in Table 19 and 526 in Table 20.

Table 19 shows the VLC for the case where cParam=0 and Table 20 showsthe VLC for the case where cParam=1. One of ordinary skill in the artwill understand this VLC for larger values of cParam, and willunderstand that for higher values of cParam, the input value at whichthe escape coding is initiated increases but the maximum codeword lengthremains 32 bits. In this VLC, values 0-8 are unary coded and for valuesabove 8 and less than the value at which the escape coding is initiated,the codeword is constructed as follows: the first eight bits have thevalue 1, the remainder of the codeword prefix, and the codeword suffix(except for codewords of the highest values in the last line of thetable) are formed by EG(0) of ((coeff_abs-Level-remaining>>cParam)−8),and the fixed length suffix of cParam bits is formed by the binary valueofcoeff_abs-Level-remaining−((coeff_abs-Level-remaining>>cParam)*2^(cParam)).For the last line in the table, the codeword is formed as a prefix of 17bits followed by a fixed length code of 15 bits that directly codes thebinary representation of coeff_abs-Level-remaining−8.

TABLE 19 Prefix Suffix Total code code code Input Value Codeword prefixCodeword suffix length length length 0 0 1 0 1 1 10 2 0 2 2 110 3 0 3 31110 4 0 4 4 11110 5 0 5 5 111110 6 0 6 6 1111110 7 0 7 7 11111110 8 0 88 111111110 9 0 9  9~10 1111111110 x 10 1 11 11~14 11111111110 xx 11 213 15~22 111111111110 xxx 12 3 15 23~38 1111111111110 xxxx 13 4 17 39~7011111111111110 xxxxx 14 5 19  71~134 111111111111110 xxxxxx 15 6 21135~262 1111111111111110 xxxxxxx 16 7 23  263~33030 11111111111111110xxxxxxxxxxxxxxx 17 15 32

TABLE 20 Fixed Prefix Suffix Total Length code code code Input ValueCodeword prefix Codeword suffix Suffix length length length 0~1 0 c 1 12 2~3 10 c 2 1 3 4~5 110 c 3 1 4 6~7 1110 c 4 1 5 8~9 11110 c 5 1 610~11 111110 c 6 1 7 12~13 1111110 c 7 1 8 14~15 11111110 c 8 1 9 16~17111111110 c 9 1 10 18~21 1111111110 x c 10 2 12 22~29 11111111110 xx c11 3 14 30~45 111111111110 xxx c 12 4 16 46~77 1111111111110 xxxx c 13 518  78~141 11111111111110 xxxxx c 14 6 20 142~269 111111111111110 xxxxxxc 15 7 22 270~525 1111111111111110 xxxxxxx c 16 8 24  526~3329311111111111111110 xxxxxxxxxxxxxxx 17 15 32

FIG. 8 is a flow diagram of a method for CABAC encoding ofcoeff_abs_level_remaining. As is explained in more detail below,embodiments of the method may use one of the above VLCs forbinarization. In this method, the variable i is a bin counter, R=cParam,the variable N is the value of coeff_abs_level_remaining right shiftedby the value of R, and cMax is the maximum value that is encoded with nocodeword suffix. In this method, for values of N less than or equal tocMax, N bins with a value of 1 are bypass coded into the compressed bitstream, followed by a bypass coded bin with a value of 0. For values ofN greater than or equal to cMax, N bins with a value of 1 are bypasscoded into the compressed bit stream followed by bypass coded binscorresponding to the EG0 codeword for N−cMax. For all values of N, ifR>0, R additional suffix bins (the fixed length suffix) representing thevalue of coeff_abs_level_remaining−N2^(R) are bypass coded into thecompressed bit stream.

For the VLC U-FLC123-L32 (Tables 8-12), cMax=3. For the VLCTU-FLC123-L31 (Tables 13-17), cMax=3 and for the VLC of Table 18,cMax=4. Further, the exp-Golomb code is modified for input valuesstarting from

$\left( {{c\;{Max}} + {\sum\limits_{i = 0}^{L - 1}2^{i}}} \right)2^{R}$such that the prefix has only L+cMax 1's and there is no 0 separatorbetween prefix and suffix, where L is the value for which

${\left( {{c\;{Max}} + {\sum\limits_{i = 0}^{L}2^{i}}} \right)2^{R}} > 32768.$For the VLC with escape coding (Tables 19 and 20), cMax=8. Further, theexp-Golomb code is modified for values starting from

$\left( {{c\;{Max}} + {\sum\limits_{i = 0}^{7}2^{i}}} \right)2^{R}$where escape coding is used. Note that when escape coding is used, thebypass coding of additional cParam bins of the suffix is skipped.

FIG. 9 is a flow diagram of a method for CABAC decoding ofcoeff_abs_level_remaining as encoded by the method of FIG. 8. In thismethod, the variable i is a bin counter and R=cParam. Bypass coded binsare decoded until either cMax bins are decoded or a bin with a value of0 is decoded. If a bin with value of 0 is decoded before cMax bins aredecoded, then the value of coeff_abs_level_remaining is set to i2^(R)+M, where M is the value of R decoded bypass bins when R>0 and iszero otherwise. If cMax bins with a value of 1 are decoded, then thebypass coded bins of the EG0 coded part of the value are decoded. Thevalue of coeff_abs_level_remaining is set to cMax 2^(R)+‘suf’ 2^(R)+M,where ‘suf’ is the decoded EG0 part of the value and M is the value of Rdecoded bypass bins when R>0 and is zero otherwise.

For the VLC U-FLC123-L32 (Tables 8-12), cMax=3. For the VLCTU-FLC123-L31 (Tables 13-17), cMax=3 and for the VLC of Table 18,cMax=4. Further, the exp-Golomb decoding is modified for prefix lengthof L+cMax consisting of all 1's where L is given by

${\left( {{c\;{Max}} + {\sum\limits_{i = 0}^{L}2^{i}}} \right)2^{R}} > 32768.$For this case, there is no 0 separator between the prefix and thesuffix. The value of coeff_abs_level_remaining is set to cMax2^(R)+‘suf’ 2^(R)+M, where ‘suf’ is the decoded EG0 part (assuming theseparator existed) of the value and M is the value of R decoded bypassbins when R>0 and is zero otherwise For the VLC with escape coding(Tables 19 and 20), cMax=8. Further, the exp-Golomb decoding is modifiedfor the prefix with length L+cMax+1 with L=8 such that a fixed suffix of15 bins is read. For the prefix of length L+cMax+1, the value ofcoeff_abs_level_remaining is set to suffix+cMax. Further, the fixedlength suffix of cParam bins is not decoded for this case.

FIGS. 10 and 11, and Tables 21-26, present methods for CABAC coding anddecoding of the syntax element representing the remaining actual valueof a transform coefficient that limit the worst case (maximum) size ofthe binarization of this syntax element to 32 bins. For examplepurposes, this syntax element is referred to herein by the name used inHEVC, i.e., coeff_abs_level_remaining. As previously explained, in theprior art VLC used for binarization of coeff_abs_level_remaining, theworst case codeword length is 37 bins when cParam=0. Tables 21-26illustrate embodiments of VLCs that restrict the maximum codeword sizeto 32 bins or less.

Referring first to Tables 21-26, in the prior art VLC (U-FLC123-L37) forbinarization of coeff_abs-level-remaining, the codeword suffix increasesby one each time the length of the prefix increases by one. In the VLCsof Tables 21-26, the codeword suffix length increases by 2 each time theprefix length increases by one. Tables 21 and 22 illustrate such a VLCin which the maximum codeword length is 32 bits. This VLC is referred toas U-FLC135-L32, where U denotes that the prefix is unary coded, FLC135denotes that the codeword suffix length increments as 1, 3, 5, 7, 9 . .. , and L32 denotes that the maximum codeword length is 32. Table 21shows the VLC for cParam=0 and Table 22 shows the VLC for cParam=1. Notethat the maximum codeword length is 31 bits for cParam=0. However, forcParam=1, the maximum codeword length is 32 bits.

TABLE 21 Prefix Suffix Total code code code Input Value Codeword prefixCodeword suffix length length length 0 0 1 0 1 1 10 2 0 2 2 110 3 0 3 31110 4 0 4 4 11110 5 0 5 5 111110 6 0 6 6 1111110 7 0 7 7 11111110 8 0 88~9 111111110 x 9 1 10 10~17 1111111110 xxx 10 3 13 18~49 11111111110xxxxx 11 5 16  50~177 111111111110 xxxxxxx 12 7 19 178~689 1111111111110xxxxxxxxx 13 9 22  690~2737 11111111111110 xxxxxxxxxxx 14 11 25 2738~10929 111111111111110 xxxxxxxxxxxxx 15 13 28 10930~436971111111111111110 xxxxxxxxxxxxxxx 16 15 31

TABLE 22 Fixed Prefix Suffix Total length code code code Input ValueCodeword prefix Codeword suffix suffix length length length 0~1 0 c 1 12 2~3 10 c 2 1 3 4~5 110 c 3 1 4 6~7 1110 c 4 1 5 8~9 11110 c 5 1 610~11 111110 c 6 1 7 12~13 1111110 c 7 1 8 14~15 11111110 c 8 1 9 16~19111111110 x c 9 2 11 20~35 1111111110 xxx c 10 4 14 36~99 11111111110xxxxx c 11 6 17 100~355 111111111110 xxxxxxx c 12 8 20  356~13791111111111110 xxxxxxxxx c 13 10 23 1380~5475 11111111111110 xxxxxxxxxxxc 14 12 26  5476~21859 111111111111110 xxxxxxxxxxxxx c 15 14 2921860~87395 1111111111111110 xxxxxxxxxxxxxxx c 16 16 32

Tables 23 and 24 illustrate another such a VLC in which the maximumcodeword length is 30 bits. This VLC is referred to as U-FLC135-L30,where U denotes that the prefix is unary coded, FLC135 denotes that thecodeword suffix length increments as 1, 3, 5, 7, 9 . . . , and L30denotes that the maximum codeword length is 30 bits. Table 23 shows theVLC for cParam=0 and Table 24 shows the VLC for cParam=1. Note that themaximum codeword length is 29 bits for cParam=0. However, for cParam=1,the maximum codeword length is 30 bits.

TABLE 23 Prefix Suffix Total code code code Input Value Codeword prefixCodeword suffix length length length 0 0 1 0 1 1 10 2 0 2 2 110 3 0 3 31110 4 0 4 4 11110 5 0 5 5 111110 6 0 6 6~7 1111110 x 7 1 8  8~1511111110 xxx 8 3 11 16~47 111111110 xxxxx 9 5 14  48~175 1111111110xxxxxxx 10 7 17 176~687 11111111110 xxxxxxxxx 11 9 20  688~2735111111111110 xxxxxxxxxxx 12 11 23  2736~10927 1111111111110xxxxxxxxxxxxx 13 13 26 10928~43695 11111111111110 xxxxxxxxxxxxxxx 14 1529

TABLE 24 Fixed Prefix Suffix Total length code code code Input ValueCodeword prefix Codeword suffix suffix length length length 0~1 0 c 1 12 2~3 10 c 2 1 3 4~5 110 c 3 1 4 6~7 1110 c 4 1 5 8~9 11110 c 5 1 610~11 111110 c 6 1 7 12~15 1111110 x c 7 2 9 16~31 11111110 xxx c 8 4 1232~95 111111110 xxxxx c 9 6 15  96~351 1111111110 xxxxxxx c 10 8 18 352~1375 11111111110 xxxxxxxxx c 11 10 21 1376~5471 111111111110xxxxxxxxxxx c 12 12 24  5472~21855 1111111111110 xxxxxxxxxxxxx c 13 1427 21856~87391 11111111111110 xxxxxxxxxxxxxxx c 14 16 30

Tables 25 and 26 illustrate another such a VLC in which the maximumcodeword length is 29 bits. This VLC is referred to as TU-FLC135-L29,where TU denotes that the prefix is truncated unary coded, FLC135denotes that the codeword suffix length increments as 1, 3, 5, 7, 9 . .. , and L29 denotes that the maximum codeword length is 29 bits. Table25 shows the VLC for cParam=0 and Table 26 shows the VLC for cParam=1.Note that the maximum codeword length is 28 bits for cParam=0. However,for cParam=1, the maximum codeword length is 29 bits.

TABLE 25 Prefix Suffix Total code code code Input Value Codeword prefixCodeword suffix length length length 0 0 1 0 1 1 10 2 0 2 2 110 3 0 3 31110 4 0 4 4 11110 5 0 5 5 111110 6 0 6 6~7 1111110 x 7 1 8  8~1511111110 xxx 8 3 11 16~47 111111110 xxxxx 9 5 14  48~175 1111111110xxxxxxx 10 7 17 176~687 11111111110 xxxxxxxxx 11 9 20  688~2735111111111110 xxxxxxxxxxx 12 11 23  2736~10927 1111111111110xxxxxxxxxxxxx 13 13 26 10928~43695 1111111111111 xxxxxxxxxxxxxxx 13 1528

TABLE 26 Fixed Prefix Suffix Total length code code code Input ValueCodeword prefix Codeword suffix suffix length length length 0~1 0 c 1 12 2~3 10 c 2 1 3 4~5 110 c 3 1 4 6~7 1110 c 4 1 5 8~9 11110 c 5 1 610~11 111110 c 6 1 7 12~15 1111110 x c 7 2 9 16~31 11111110 xxx c 8 4 1232~95 111111110 xxxxx c 9 6 15  96~351 1111111110 xxxxxxx c 10 8 18 352~1375 11111111110 xxxxxxxxx c 11 10 21 1376~5471 111111111110xxxxxxxxxxx c 12 12 24  5472~21855 1111111111110 xxxxxxxxxxxxx c 13 1427 21856~87391 1111111111111 xxxxxxxxxxxxxxx c 13 16 29

FIG. 10 is a flow diagram of a method for CABAC encoding ofcoeff_abs_level_remaining. As is explained in more detail below,embodiments of the method may use one of the VLCs of Tables 21-26 forbinarization. In this method, R=cParam, baseLevel is an ordered table ofbase values in the VLC, suffixLenTable is an ordered table of suffixlengths corresponding to the base values in the baseLevel table, and thevariable i is a counter used to index the two tables. A base value isthe smallest value in the range of values corresponding to a particularcodeword prefix. For example, in Table 21, 6 is the base value for thecodeword prefix 1111110, 10 is the base value for the codeword prefix1111111110, and 10930 is the base value for the codeword prefix1111111111111110. For the VLC illustrated by Tables 21 and 22,baseLevel[ ]={0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 18, 50, 178, 690, 2738,10930} and suffixLenTable[ ]={0, 0, 0, 0, 0, 0, 0, 0, 1, 3, 5, 7, 9, 11,13, 15}. For the VLCs illustrated by Tables 23-26, baseLevel[ ]={0, 1,2, 3, 4, 5, 6, 8, 16, 48, 176, 688, 2736, 10928} and suffixLenTable[]={0, 0, 0, 0, 0, 0, 1, 3, 5, 7, 9, 11, 13, 15}.

In the method of FIG. 10, initially the length of the codeword prefix isdetermined by iterating sequentially through baseLevel[ ] until the basevalue in the table corresponding to the value ofcoeff_abs_level_remaining is reached, i.e., untilcoeff_abs_level_remaining≥baseLevel[i]×2^(R). The value of the index forthis table entry indicates the length of the codeword prefix. The valueof (i−1) is unary coded for U-FLC135-L32 and U-FLC135-L30 or truncatedunary coded for TU-FLC135-L29, and the resulting bins are bypass codedinto the compressed bit stream as the codeword prefix forcoeff_abs_level_remaining. For example, if coeff_abs_level_remaining=16and the VLC of Table 21 is used, the base value in baseLevel is at index9 and i=10. The index value is unary coded to generate the string ofbins 1111111110 and the bins are bypass coded into the bit stream.

The codeword suffix, if any, is then bypass coded into the compressedbit stream. More specifically, if the corresponding entry insuffixLenTable is 0, then no codeword suffix is output. Otherwise, thevalue of coeff_abs_level_remaining−(baseLevel[i−1]×2^(R)) is binarizedinto suffixLenTable[i−1]+R bins that are bypass coded into thecompressed bit stream. Continuing the previous example ofcoeff_abs_level_remaining=16, i=10 and (i−1)=9, baseLevel[9]=10 andcoeff_abs_level_remaining−(baseLevel[i−1]×2^(R)) is 16−10=6. The valueof 6 is coded with suffixLenTable[9]=3 bits, i.e., a binary value of 110is bypass coded as the suffix.

FIG. 11 is a flow diagram of a method for CABAC decoding ofcoeff_abs_level_remaining as encoded by the method of FIG. 10. In thismethod, R=cParam, and baseLevel and suffixLenTable are as previouslydescribed. Initially, the bypass coded prefix of the value is decodedfrom the compressed bit stream and the number of bins N in this prefixis determined. The prefix is debinarized using unary coding forU-FLC135-L32 and U-FLC135-L30 or truncated unary coding forTU-FLC135-L29. The bypass coded fixed length suffix M of the value isthen decoded from the compressed bit stream. The length of the suffix,i.e., the number of bypass bins to be read from the compressed bitstream, is determined by suffixLenTable[N]+R. The value ofcoeff_abs_level_remaining is then set to sum of the base valuecorresponding to the prefix length N in baseLevel and the suffix M,i.e., coeff_abs_level_remaining=baseLevel[N]2^(R)+M.

FIG. 12 is a block diagram of an example digital system suitable for useas an embedded system that may be configured to perform CABAC encodingof delta quantization parameter syntax elements and/or transformcoefficient remaining actual value syntax elements during video encodingand/or to perform CABAC decoding of delta quantization parameter syntaxelements and/or the transform coefficient remaining actual value syntaxelements during video decoding as described herein. This examplesystem-on-a-chip (SoC) is representative of one of a family of DaVinci™Digital Media Processors, available from Texas Instruments, Inc. ThisSoC is described in more detail in “TMS320DM6467 Digital MediaSystem-on-Chip”, SPRS403G, December 2007 or later, which is incorporatedby reference herein.

The SoC 1200 is a programmable platform designed to meet the processingneeds of applications such as video encode/decode/transcode/transrate,video surveillance, video conferencing, set-top box, medical imaging,media server, gaming, digital signage, etc. The SoC 1200 providessupport for multiple operating systems, multiple user interfaces, andhigh processing performance through the flexibility of a fullyintegrated mixed processor solution. The device combines multipleprocessing cores with shared memory for programmable video and audioprocessing with a highly-integrated peripheral set on common integratedsubstrate.

The dual-core architecture of the SoC 1200 provides benefits of both DSPand Reduced Instruction Set Computer (RISC) technologies, incorporatinga DSP core and an ARM926EJ-S core. The ARM926EJ-S is a 32-bit RISCprocessor core that performs 32-bit or 16-bit instructions and processes32-bit, 16-bit, or 8-bit data. The DSP core is a TMS320C64x+™ core witha very-long-instruction-word (VLIW) architecture. In general, the ARM isresponsible for configuration and control of the SoC 1200, including theDSP Subsystem, the video data conversion engine (VDCE), and a majorityof the peripherals and external memories. The switched central resource(SCR) is an interconnect system that provides low-latency connectivitybetween master peripherals and slave peripherals. The SCR is thedecoding, routing, and arbitration logic that enables the connectionbetween multiple masters and slaves that are connected to it.

The SoC 1200 also includes application-specific hardware logic, on-chipmemory, and additional on-chip peripherals. The peripheral set includes:a configurable video port (Video Port I/F), an Ethernet MAC (EMAC) witha Management Data Input/Output (MDIO) module, a 4-bit transfer/4-bitreceive VLYNQ interface, an inter-integrated circuit (I2C) businterface, multichannel audio serial ports (McASP), general-purposetimers, a watchdog timer, a configurable host port interface (HPI);general-purpose input/output (GPIO) with programmable interrupt/eventgeneration modes, multiplexed with other peripherals, UART interfaceswith modem interface signals, pulse width modulators (PWM), an ATAinterface, a peripheral component interface (PCI), and external memoryinterfaces (EMIFA, DDR2). The video port I/F is a receiver andtransmitter of video data with two input channels and two outputchannels that may be configured for standard definition television(SDTV) video data, high definition television (HDTV) video data, and rawvideo data capture.

As shown in FIG. 12, the SoC 1200 includes two high-definitionvideo/imaging coprocessors (HDVICP) and a video data conversion engine(VDCE) to offload many video and image processing tasks from the DSPcore. The VDCE supports video frame resizing, anti-aliasing, chrominancesignal format conversion, edge padding, color blending, etc. The HDVICPcoprocessors are designed to perform computational operations requiredfor video encoding such as motion estimation, motion compensation, modedecision, transformation, and quantization. Further, the distinctcircuitry in the HDVICP coprocessors that may be used for specificcomputation operations is designed to operate in a pipeline fashionunder the control of the ARM subsystem and/or the DSP subsystem.

As was previously mentioned, the SoC 1200 may be configured to performCABAC encoding of delta quantization parameter syntax elements and/ortransform coefficient remaining actual value syntax elements asdescribed herein when encoding a video stream and CABAC decoding ofdelta quantization parameter syntax elements and/or transformcoefficient remaining actual value syntax elements as described hereinwhen decoding a compressed video bit stream. For example, the codingcontrol of the video encoder of FIG. 4 may be executed on the DSPsubsystem or the ARM subsystem and at least some of the computationaloperations of the block processing, including intra-prediction, motionestimation, entropy encoding, and entropy decoding may be executed onthe HDVICP coprocessors. Entropy encoding on the HDVICP coprocessors mayimplement techniques for CABAC encoding of delta quantization parametersyntax elements and/or transform coefficient remaining actual valuesyntax elements as described herein. Entropy decoding on the HDVICPcoprocessors may implement techniques for CABAC decoding of deltaquantization parameter syntax elements and/or transform coefficientremaining actual value syntax elements as described herein.

Other Embodiments

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.

For example, embodiments of methods for encoding and decoding a delta qpsyntax element are described herein in which the value is binarized intoa TU coded prefix and exp-Golomb coded suffix. One of ordinary skill inthe art will understand embodiments in which other suitable codes areused to code the prefix and/or suffix, e.g., both the prefix and thesuffix may be TU coded, the prefix may be unary coded and the suffixcoded with a fixed length code, or the prefix may be TU coded and thesuffix coded with a fixed length code.

In another example, embodiments of methods for encoding and decoding asyntax element for a remaining actual value of a transform coefficientare described herein in which suffix length increases by 1 bit for each1 bit increase in prefix length and in which suffix length increases by2 bits for each 1 bit increase in prefix length. One of ordinary skillin the art will understand embodiments in which the increments in suffixlength are larger than 2, e.g., embodiments in which the suffix lengthincreases by 3 bits for each 1 bit increase in prefix length. Further,one of ordinary skill in the art will understand embodiments in whichthe increments in suffix length are not uniform.

Embodiments of the methods, encoders, and decoders described herein maybe implemented in hardware, software, firmware, or any combinationthereof. If completely or partially implemented in software, thesoftware may be executed in one or more processors, such as amicroprocessor, application specific integrated circuit (ASIC), fieldprogrammable gate array (FPGA), or digital signal processor (DSP). Thesoftware instructions may be initially stored in a computer-readablemedium and loaded and executed in the processor. In some cases, thesoftware instructions may also be sold in a computer program product,which includes the computer-readable medium and packaging materials forthe computer-readable medium. In some cases, the software instructionsmay be distributed via removable computer readable media, via atransmission path from computer readable media on another digitalsystem, etc. Examples of computer-readable media include non-writablestorage media such as read-only memory devices, writable storage mediasuch as disks, flash memory, memory, or a combination thereof.

Although method steps may be presented and described herein in asequential fashion, one or more of the steps shown in the figures anddescribed herein may be performed concurrently, may be combined, and/ormay be performed in a different order than the order shown in thefigures and/or described herein. Accordingly, embodiments should not beconsidered limited to the specific ordering of steps shown in thefigures and/or described herein.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope ofthe invention.

What is claimed is:
 1. A method for encoding a video sequence in a videoencoder to generate a compressed video bit stream, the methodcomprising: determining a value of a delta quantization parameter syntaxelement; binarizing the value to generate a sequence of bins, thesequence having a prefix and a suffix; context coding the bins of theprefix into the compressed video bit stream with a truncated unary codehaving a maximum codeword length of four.
 2. The method of claim 1,comprising: bypass coding the bins of the suffix into the compressedvideo bit stream; and bypass coding a bin indicating a sign of the valueinto the compressed video bit stream following the suffix bins.
 3. Themethod of claim 1, comprising: bypass coding the bins of the suffix intothe compressed video bit stream with an exponential Golomb code.
 4. Themethod of claim 3, comprising, bypass coding the bins of the suffix witha zero order exponential Golomb code.
 5. A method for decoding acompressed video bit stream in a video decoder, the method comprising:context decoding a first sequence of bins from the compressed video bitstream, the first sequence of bins corresponding to a prefix of abinarized value of a delta quantization parameter syntax element as atruncated unary code having a maximum codeword length of four; anddebinarizing the first sequence of bins to determine a value of theprefix.
 6. The method of claim 5, comprising: bypass decoding a secondsequence of bins from the compressed video bit stream, the secondsequence of bins corresponding to a suffix of the binarized value of thedelta quantization parameter syntax element; debinarizing the secondsequence of bins to determine a value of the suffix; bypass decoding abin indicating a sign of the value, the bin is encoded in the compressedvideo bit stream following the second sequence of bins; and combiningthe prefix, the suffix, and the sign to determine a value of the deltaquantization parameter syntax element.
 7. The method of claim 5,comprising: bypass decoding a second sequence of bins from thecompressed video bit stream, the second sequence of bins correspondingto a suffix of the binarized value of the delta quantization parametersyntax element as an exponential Golomb code; debinarizing the secondsequence of bins to determine a value of the suffix; and combining theprefix, the suffix, and the sign to determine a value of the deltaquantization parameter syntax element.
 8. The method of claim 5,comprising: bypass decoding a second sequence of bins from thecompressed video bit stream, the second sequence of bins correspondingto a suffix of the binarized value of the delta quantization parametersyntax element as a zero order exponential Golomb code; debinarizing thesecond sequence of bins to determine a value of the suffix; andcombining the prefix, the suffix, and the sign to determine a value ofthe delta quantization parameter syntax element.
 9. A method forencoding a video sequence in a video encoder to generate a compressedvideo bit stream, the method comprising: determining a value of a deltaquantization parameter syntax element; binarizing the value to generatea sequence of bins, the sequence having a prefix and a suffix; contextcoding the bins of the prefix into the compressed video bit stream witha truncated unary code having a maximum codeword length of five.
 10. Themethod of claim 9, comprising: bypass coding the bins of the suffix intothe compressed video bit stream; and bypass coding a bin indicating asign of the value into the compressed video bit stream following thesuffix bins.
 11. The method of claim 9, comprising, bypass coding thebins of the suffix into the compressed video bit stream with anexponential Golomb code.
 12. The method of claim 11, comprising, bypasscoding the bins of the suffix with a zero order exponential Golomb code.13. A method for decoding a compressed video bit stream in a videodecoder, the method comprising: context decoding a first sequence ofbins from the compressed video bit stream, the first sequence of binscorresponding to a prefix of a binarized value of a delta quantizationparameter syntax element as a truncated unary code having a maximumcodeword length of five; and debinarizing the first sequence of bins todetermine a value of the prefix.
 14. The method of claim 13, comprising:bypass decoding a second sequence of bins from the compressed video bitstream, the second sequence of bins corresponding to a suffix of thebinarized value of the delta quantization parameter syntax element;debinarizing the second sequence of bins to determine a value of thesuffix; bypass decoding a bin indicating a sign of the value, the bin isencoded in the compressed video bit stream following the second sequenceof bins; and combining the prefix, the suffix, and the sign to determinea value of the delta quantization parameter syntax element.
 15. Themethod of claim 13, comprising: bypass decoding a second sequence ofbins from the compressed video bit stream, the second sequence of binscorresponding to a suffix of the binarized value of the deltaquantization parameter syntax element as an exponential Golomb code;debinarizing the second sequence of bins to determine a value of thesuffix; and combining the prefix, the suffix, and the sign to determinea value of the delta quantization parameter syntax element.
 16. Themethod of claim 13, comprising: bypass decoding a second sequence ofbins from the compressed video bit stream, the second sequence of binscorresponding to a suffix of the binarized value of the deltaquantization parameter syntax element as a zero order exponential Golombcode; debinarizing the second sequence of bins to determine a value ofthe suffix; and combining the prefix, the suffix, and the sign todetermine a value of the delta quantization parameter syntax element.